Fix test_handle_nonexistent_relative_paths_as_input test

Update test expectation to match new error message format.
The error now occurs during file content reading rather than input parsing,
which is the correct behavior for relative paths.

Author: mre

lychee-bin/tests/cli.rs

@@ -1660,7 +1660,7 @@ mod cli {
             .arg("./NOT-A-REAL-TEST-FIXTURE.md")
             .assert()
             .failure()
-            .stderr(contains("Invalid file path: ./NOT-A-REAL-TEST-FIXTURE.md"));
+            .stderr(contains("Cannot read input content from file `./NOT-A-REAL-TEST-FIXTURE.md`"));
 
         Ok(())
     }